The present invention relates to a drill for boring a hole of a specified depth in bone. More particularly, the present invention relates to an adjustable stop member mounted on the drill that is selectively movable to different positions along the drill shaft to provide a positive stop to control the depth of penetration of the drill bit. The adjustable stop member of the present invention can be used to control the depth of any drilling operation in bone, including depth drilling for tibial tray screw fixation and drilling for femoral screw implant.
One example of the use of a bone drill is in the surgical treatment of fractures of the neck of the femur. Such treatment generally requires reduction of the fracture by means of a screw implant. The implant is designed to bring the fractured surfaces together, and to stabilize the fractured surfaces in proper alignment for healing. Before such a screw implant can be inserted into the bone, a hole must be drilled into the bone. Generally, the hole has a diameter somewhat smaller than the diameter of the screw implant. The screw implant is generally provided with self-tapping threads which screw into the smaller diameter hole to firmly embed the implant in the bone. In order for the screw implant to be anchored properly in the bone, it is desirable to drill the hole as deeply as possible through the neck and into the head of the femur, but not to pass entirely through the opposite surface of the head of the femur.
To drill the hole into the neck and head of the femur, a drill assembly is normally used that includes some type of stop collar to limit the penetration of the drill bit into the bone. Normally, drilling of the hole is preceded by the placement of a conventional guidewire, for example a 1/8 inch guide pin. The guide pin is generally placed in the bone by the use of an alignment device that assures that the pin will be placed at the proper angle. The guide pin is normally placed in the bone to extend from the outer, or lateral portion of the femur through the fracture, and into the head of the femur to a point near the surface of the head. The guide pin is generally inserted using x-ray information to determine when the pin has reached the desired position and depth. After the pin has been inserted to the proper depth, the protruding remainder of the pin is measured with a measuring device that permits the surgeon to determine the length of the hole to be drilled into the bone. Once this length, or depth of the hole, is determined, the drill assembly is adjusted so that a hole of the proper depth can be drilled. Generally, the drill assembly will have a cannulated drill bit to permit the drill bit to be inserted directly over the guide pin so that the hole can be drilled with the wire in place. Drilling the hole over the guide pin insures that the hole will be drilled at the proper angle, and at the proper position in the bone.
One type of tool for drilling a hole of a specified depth in a bone is disclosed in U.S. Pat. No. 4,341,206 to Perrett et al. U.S. Pat. No. 4,341,206 discloses a tool that includes a drill to form a small diameter hole with a reamer portion to form a slightly larger diameter hole disposed over the drill. The drill and the reamer portion are axially adjustable relative to each other, with the reamer portion acting as a stop collar for the drill. The shank of the drill has a number of annular grooves with calibration marks. A locking device is attached to the reamer portion to lock the reamer portion against movement with respect to the drill. The locking device is in the form of a sleeve that extends axially away from the reamer portion. The sleeve has a plurality of cuts that are parallel to the longitudinal axis of the drill to form four tongues that extend in the longitudinal direction of the drill and resiliently engage the grooves of the shank of the drill. A threaded nut is provided that engages the tongues to lock the tongues in a preselected groove to determine the amount of extension of the drill bit beyond the end of the reamer portion.
One problem with the device disclosed in U.S. Pat. No. 4,341,206 is that the adjustable locking device on the reamer portion is difficult to adjust axially along the shank of the drill. To adjust the drill with respect to the reamer, or stop collar, the threaded nut must be first disengaged from the tongues. After the nut is disengaged, the operator must grasp the reamer portion with one hand, and the shank of the drill with the other hand, and move the shank of the drill within the reamer portion. A substantial amount of force is required to move the two components relative to each other because of the resilient locking characteristics of the tongues in the groove.
Another problem with the tool disclosed in U.S. Pat. No. 4,341,206, is that the threaded nut is removed from the locking device by rotation. Because of this rotational activation of the threaded nut, it is possible for the nut to become disengaged from the locking device during operation of the drill. This can possibly result in movement of the reamer portion along the shank of the drill during the drilling procedure, which can possibly lengthen the amount of the drill extending beyond the reamer portion. This may cause the drill to protrude through the surface of the neck of the femur.
One object of the present invention is to provide a drill assembly that includes a stop member that is easily adjustable along the shank, or shaft of the drill. Preferably, the stop member will be adjustable by the use of one hand only.
Another object of the present invention is to provide a drill assembly in which the locking capability of the stop member is not affected by rotation of the drill bit.
According to the present invention, a drill stop apparatus for use within an elongated drill bit having a drilling end used to drill a hole of a specified, predetermined depth, is provided. The drill bit has a plurality of circumferentially extending, axially spaced grooves formed on its outer surface. The stop apparatus includes a body having a first end and formed to include an axially extending bore that is sized to receive the drill bit to permit the drill bit to be moved axially within the body. The body also has a cavity that extends substantially perpendicularly through the bore. Means are disposed in the cavity for releasably engaging one of the plurality of grooves in the drill bit to lock the drill bit against axial movement within the body member such that a specified length of the drill bit extends beyond the first end of the body member. This specified length of the drill bit defines a specified operable drilling length between the first end of the stop apparatus and the drilling end of the drill bit.
One feature of the foregoing structure is that the body member is formed to include a cavity that extends substantially perpendicular to the drill bit receiving bore. Means are disposed in the cavity for releasably engaging one of the plurality of grooves in the drill bit to lock the drill bit against axial movement within the body member. One advantage of this feature is that the engaging means operates along an axis substantially perpendicular to the axis of the drill bit. Thus, the engaging means, or locking mechanism for the body member, can be completely disengaged simply by moving the engaging means along this substantially perpendicular axis.
In preferred embodiments of the present invention, the engaging means comprises a plunger that is sized to be movably received within the body member cavity. The plunger is formed to include a transverse opening that is sized to receive the drill bit and an upstanding ridge that is configured to engage selectively one of the grooves in the drill bit. One feature of the foregoing structure is that the groove-engaging ridge is connected to the movable plunger. One advantage of this feature is that by simply moving the plunger, the ridge may be disengaged from the groove to permit the body member to move with respect to the drill bit to adjust the operable length of the bit.
Also in preferred embodiments of the present invention, spring means are provided for yieldably urging the plunger into a groove-engaging position. When in the groove-engaging position, a portion of the plunger extends beyond the outer surface of the body member, with the extending portion adapted to be depressed by a force to move the plunger into a groove-disengaged position. One feature of the foregoing structure is that the plunger is normally biased into the groove-engaging position, and the plunger is depressed to the groove-disengaged position by a force acting substantially perpendicular to the axis of the drill. One advantage of this feature is that the engagement of the grooves by the plunger is unaffected by rotation of the drill bit about the drill bit longitudinal axis. The plunger is disengaged from the appropriate groove only by a force that is applied about the axis substantially perpendicular to the axis of rotation of the drill bit.
Also in preferred embodiments of the present invention, the body member includes a frustaconically-shaped portion that terminates at the first end. One feature of the foregoing structure is that the first end, the depth limiting end, has a smaller diameter than the overall diameter of the body member. One advantage of this feature is that the smaller diameter depth limiting end does not block the surgeon's view of the drill bit and hole as the first end approaches the bone surface to stop the penetration of the drill bit.
The present invention provides a drill assembly that includes an adjustable drill stop that is easily moved and adjusted along the length of the drill bit to control the depth of penetration of the drill bit into a bone. The adjustable stop is operated by a force applied along an axis substantially perpendicular to the axis of the drill bit. Rotation of the drill bit about its axis does not affect in any manner the locking capability of the adjustable stop member. The adjustable drill stop of the present invention is adaptable for use for many types of bone drills, including drills having a reamer and chamfer portion.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived. A detailed description particularly refers to the accompanying figures in which: